Interpretive Summary: Selenium consumed in amounts greater than the dietary requirement decreases the risk of colon, prostate and lung cancer. Beef is the greatest source of selenium in the North American diet but beef selenium concentrations vary depending on soil selenium concentrations at the site of origin. To determine factors that affect selenium accumulation in beef, cattle were purchased from areas of low or high soil selenium. Each group of cattle was divided in half and fed, for 150 days, a diet (alfalfa hay and wheat) composed of feeds grown in an area of low or high soil selenium. Animals were checked periodically for signs of selenium toxicity and none were detected in any of the dietary groups. Cattle fed the high selenium diets accumulated the most selenium in beef, and cattle purchased from an area with high soil selenium accumulated more than animals from a low-selenium area. Cattle from a high selenium area fed a high selenium diet had selenium concentrations in the beef of more than 10 times the national average. Cattle from a low selenium area accumulated more selenium in the kidney than animals from the high selenium area representing a possible adaptation to living in high selenium areas. The results of this study show that beef can be enriched in selenium by feeding diets high in selenium, and selenium toxicity is not a problem in relatively short- term feeding studies.

Technical Abstract:
The single most important dietary source of Se is beef. The Se content of beef varies, and cattle with above average Se concentrations may potentially be supplemental sources of dietary Se. To examine factors affecting Se accumulation in beef, 16 steers (initial wt 374.4 +/- 33.7 kg) from a high or moderate-Se background were fed, in a 2x2 factorial design, diets high or moderate in Se (11.9 or 0.62 mg Se/kg diet). Diets contained 50% alfalfa, 25% wheat, and 25% corn on a dry matter basis. All dietary Se was from natural ingredients, and Se in the high-Se diet was primarily from high-Se wheat and alfalfa hay. A loin muscle biopsy was taken at the start of the trial to determine initial Se content of beef. Steers were slaughtered after 14 wks of the trial, and edible carcass (round, sirloin, shoulder clod and ribeye) and organ samples were collected. Diets did not affect growth or feed intake (P>.05) and Se toxicity symptoms were not observed. Different cuts of meat had similar Se concentrations and the Se content of all cuts was increased by both high dietary Se and high-Se background. Except for liver and kidney, Se in tissues was increased by seleniferous background (P<.02) and high dietary Se (P<.001). Kidney Se concentrations of animals fed the high- Se diet were lowest in animals from a high-Se background (P=.04), suggesting a lack of adaptation to the high-Se diet. These results demonstrate that cattle from high-Se backgrounds fed high-Se diets produce beef highest in Se.